Decreasing the weight of motor vehicles to provide better fuel economy, and increasing the strength of motor vehicles to provide greater protection to occupants during a collision are both desirable goals. These goals, however, are often in conflict and compromises between decreasing weight and increasing strength are often made in the design of motor vehicles. The ultimate goal is to provide motor vehicles that are sufficiently strong to provide adequate protection for occupants in the event of a collision and are also sufficiently light in weight to maximize fuel economy.
A typical motor vehicle has a frame upon which body panels and engine and suspension components are mounted. The frame also supports the vehicle's bumpers and provides protection to vehicle occupants during a collision. The overall protection provided by the frame is dependent upon the rigidity and buckle strength of individual structural members that make up the frame. Many of the structural members, especially those upon which the vehicle's bumpers are mounted are tubular or have a non-circular hollow cross-section. The rigidity and buckle strength of the individual tubular or non-circular hollow structural members is normally dependent upon the sidewall thickness of the structural member. Increasing the sidewall thickness increases the strength of the structural member but also increases the weight of the structural member, while decreasing the sidewall thickness decreases the weight but also decreases the strength.
In summary, the frame of a motor vehicle comprises a large portion of the total weight of the motor vehicle and also comprises a large portion of the protection provided by the motor vehicle to vehicle occupants during collisions. Accordingly, there is a need for reducing the weight of the tubular or non-circular hollow structural members of the frame without substantially reducing the rigidity and buckle strength of the structural members. There is also a need for increasing the strength of the tubular or non-circular hollow structural members without substantially increasing the weight or sidewall thickness of the structural member.